1. Field of the Invention
The present invention relates to a high density, and more particularly, to a high density disc in which a data area is set to secure compatibility in the same drive while maintaining a superior recording and/or reproducing feature and a recording capacity.
2. Description of the Related Art
In general, an optical disc is widely used as an information recording medium of an optical pickup apparatus to record and/or reproduce information in a non-contact manner. The optical discs are divided into compact discs (CDs) and digital versatile discs (DVDs) according to its information recording capacity. Further, mini discs (MD) having a diameter of 65 mm or less may be added to the above classification.
These optical discs can be further divided into read only discs, such as CD-ROMs (read only memory) and DVD-ROMs, and recordable discs, such as CD-RWs and DVD-RAMs.
A CD is 1.2 mm thick and formed of polycarbonate (PC). The CD is reproduced by using a laser diode having a wavelength of 780 nm and has a track pitch of 1.6 μm and a recording capacity of 650 MB on a single side having an outer diameter of 120 mm.
In the case of a DVD, a polycarbonate reinforcement plate having a thickness of 0.6 mm is attached to a substrate having a thickness of 0.6 mm, thus forming a 1.2 mm thickness, so that the DVD is compatible with a CD-ROM drive. When a DVD is a single side disc of a 120 mm diameter, the recording capacity amounts to 4.7 GB. Also, a double side DVD having a recording capacity of 9.4 GB is formed by combining two 0.6 mm discs. The DVD is reproduced by a laser diode of a 650 nm wavelength and an objective lens having a numerical aperture (NA) of 0.65, and has a track pitch of about 0.74 μm. Also, a DVD having a diameter of 80 mm has a recording capacity of 1.47 GB corresponding to the recording capacity of two CDs.
Further, a high density disc, that is, an HD-DVD, has a recording capacity of about 25 GB on a single side having a 120 mm diameter. The HD-DVD is recorded and/or reproduced by using a laser diode of a 400 nm wavelength and an objective lens having an NA of 0.85, and has a track pitch of about 0.3 μm. Also, an HD-DVD having a 80 mm diameter has a recording capacity of about 7.8 GB.
Meanwhile, an HD TV requires a disc which can record and/or reproduce a 135 minute movie for HD. The disc for HD requires a recording capacity to record and/or reproduce about 23 GB or more on a single side of a disc having a 120 mm diameter, although not standardized yet.
The specifications of a CD and DVD are shown below in Table 1.
TABLE 1CDDVDDiameter of disc (mm)120120Thickness of disc (mm)1.21.2Thickness of information substrate1.20.6(mm)Track pitch (μm)1.60.74Size of minimum pit (μm)0.830.4Wavelength of laser beam (μm)780635/650NA of objective lens (NA)0.50.65Capacity of single side disc (GB)0.654.7(1.47)
FIG. 1 illustrates the structure of a disc 1 such as a CD or DVD. Referring to the drawing, the high density disc 1 can be divided into a center hole 10, a clamping area 20 to accommodate the high density disc 1 on a turntable (63 of FIG. 2) of a reproduction drive to be described later, a lead-in area 30 from which data begins to record, a data area 40 to record user data, and a lead-out area 50 at which the data area 40 ends.
Reproduction only data, used for purposes such as the size of the high density disc 1, the number of tracks on a surface to be read, or copy protection information, can be recorded in the lead-in area 30. The data area 40 is an area where a user can record and/or reproduce information. Also, other information related to the high density disc is recorded in the lead-out area 50. Reference numeral 25 denotes an area where a stack ring (not shown) is formed to prevent deterioration of productivity due to control of disc recording surfaces when discs manufactured during a disc injection step are stacked.
FIG. 2 illustrates a disc chucking apparatus of the disc 1. Here, the chucking apparatus of the high density disc 1 includes a spindle motor 60 to rotate the high density disc 1, a turntable 63 fixed to a rotation shaft of the spindle motor 60, on which the high density disc 1 is placed, and a clamping member 65 closely pressing the high density disc 1 against the turntable 63. As the high density disc 1 is closely pressed and fixed between the turntable 63 and the clamping member 65, when the high density disc 1 is rotated by the spindle motor 60, information can be reproduced without the high density disc 1 trembling.
A protruding portion 63a protruding from the center of the turntable 63 is inserted in the center hole 10 of the high density disc 1. A magnetic body 64 is provided at the turntable 63 or at the clamping member 65 so that the high density disc 1 is fixed by a magnetic force of the magnetic body 64. Here, an area of the high density disc 1 contacting the clamping member 65 is the clamping area 20.
In conventional CDs or DVDs, when the outer diameter (Φt) of the entire disc is 120 mm or 80 mm, the size of the center hole 10 is specified to be a diameter (Φh) of 15 mm. Also, the outer diameter of the clamping area 20 is specified to be a diameter (Φc) of about 32.7 mm.
The lead-in area 30 has a diameter of 46–50 mm or 45.2–48 mm for a CD or DVD, respectively. The inner diameter (Φd) of the data area 40 is 48.2 mm. In the case of a DVD+RW, the inner diameter (Φi) of the lead-in area 30 is specified to be 44.0 mm. For a disc having a diameter of 120 mm, the outer diameter (Φoe) of the lead-out area 50 can be up to 117 mm in length. For a disc having a diameter of 80 mm, the outer diameter (Φoe) of the lead-out area 50 is up to 78 mm in length.
However, when the overall diameter of a disc is small, for example, the overall diameter (Φt) of a disc is 64 mm, if the position (Φd) where user data starts is set to have a diameter of 48.2 mm, as in the CD or DVD, the data recording capacity is not sufficient. Further, if the above specifications are applied to a disc having an overall diameter of 50 mm, substantially no data area exists. If the diameter of the center hole 10 is formed to be less than 15 mm to compensate for the insufficient data area, a problem of compatibility with a disc drive for a disc having an overall diameter of 120 mm or 80 mm occurs.
There is a method of decreasing the size of the clamping area 20 to secure the recording capacity of a disc. However, since the diameter (Φc) of the clamping area 20 is limited to be within 33.0 mm, it is difficult to secure compatibility with a disc drive and simultaneously increase the recording capacity. The size of the clamping area 20 is determined by a deviation factor of a disc, the number of rotations of the spindle motor 60, or the clamping force of a disc. Since a vibration feature of a disc deteriorates when the clamping area 20 is reduced, there is a certain limit in decreasing the clamping area 20. Presently, most spindle motors 60 for CD-ROMs or DVD-RAMs have an outer diameter of 28.0 mm or less while the outer diameter of the turntable 63 is 30.0 mm or less, which satisfies the size of the clamping area of a disc, that is, a diameter of 33.0 mm or less.
Since the conventional high density disc such as a CD or DVD is large, a drive for the high density disc is also large and difficult to carry. Considering portability first, a high density disc having a smaller diameter must be used. When the diameter of a disc is decreased, recording capacity decreases so that data cannot be recorded sufficiently. Also, repetition of recording is restricted and accordingly free editing is restricted, which prevents an increase of value of data. Thus, new specifications of a high density disc are needed so that a high density recording capacity is secured and simultaneously a small disc can be compatibly recorded and/or reproduced in the same drive.